1. Field of the Invention
The present invention relates in general to control systems for controlling an automotive automatic transmission, and more particularly to control systems of a type which corrects a line pressure of the automatic transmission in accordance with a given factor of fuel supplied to an associated internal combustion engine with which the transmission is incorporated.
2. Background of the Invention
As is known, most of the late automatic transmissions incorporated with an automotive engine are controlled by a mechanically operated hydraulic circuit. Recently, as is shown in JIDOUSHA KOGAKU ZENSHO VOLUME 9 issued from SANKAIDO Co., Ltd on Nov. 20, 1980, some of the automatic transmissions of such type have a computer-aided control unit which assists the control by the hydraulic circuit. In the transmissions of this type, a precise control for gear changes is effected by carrying out ON-OFF operation of a shift solenoid and the line pressure is controlled to a certain value by making a line pressure solenoid carry out a so-called duty ratio operation. That is, by the work of the computer-aided control unit, the target value of the line pressure is derived one after another in accordance with a load applied to the engine, and the duty ratio of the line pressure solenoid is controlled in accordance with the target value.
Accordingly, the clutch operating hydraulic pressure, which is given by reducing the line pressure at a given ratio, is controlled using the load as a parameter. Usually, since the transmission torque of each clutch is known, the clutch operating hydraulic pressure is so determined as to create the optimum value of the transmission torque.
However, the torque generated by the engine differs between two cases, one being a case wherein the engine is operated on low octane gasoline and the other being a case wherein the engine is operated on high octane gasoline. In particular, in conventional control systems, such as the system as disclosed in Japanese Patent First Provisional Publication 58-143169, wherein the ignition timing is controlled in accordance with the octane value of gasoline supplied to the engine, the difference of the torque between the low octane gasoline and the high octane gasoline is very large. This will be easily understood from the graph of FIG. 8.
Accordingly, if high octane gasoline is supplied to an engine whose transmission has the clutch operating hydraulic pressure set up based on low octane gasoline, the torque applied to clutches upon gear change becomes greater than a predetermined desired value causing excessive slippage of the clutches. Of course, this phenomenon shortens the life of the clutches.
On the contrary, if low octane gasoline is supplied to an engine whose transmission has the clutch operating hydraulic pressure set up based on high octane gasoline, the torque applied to the clutch upon gear change becomes lower than the predetermined value causing lack of suitable slippage of the clutches. This phenomenon increases the gear change shock of the transmission.